Image sensors are widely used in various electronic devices, such as digital still cameras, digital video cameras, cellular phones, security cameras, medical devices and automobile electronics, The image quality of an image sensor is subject to several factors. One of the factors is temporal random noise (RN), including readout noise and quantization noise. RN incurred in an analog readout circuit is one key parameter for determining the quality of an image sensor. Existing methods suffer low frame rate problem or additional hardware cost. It may therefore be desirable to have a novel architecture to address the above mentioned issues.